Investigations into the role of surface antigen of B and T lymphocytes in determining inherited differences in the susceptibility of chickens to viral oncogenesis of lymphocytes will be continued. In a new experimental design, chickens of all nine genotypes at the Ly-4 and Th-1 loci will be compared for susceptibility to oncogenesis by Marek's disease herpesvirus. Similar tests with lymphoid leukosis and sarcoma viruses will be concentrated on tumor regression, and in addition will involve Bu-1. The same design will be used to test and confirm associations of Bu-1, Th-1 and Ly-4 genotypes with cellular and humoral immune responsiveness, and with lymphoproliferative potential, in extension of our preliminary findings. The mechanisms of the associations will be investigated by in vivo cell transfers, and by in vitro studies of normal and transformed lymphocytes, including antigen co-capping, cytotoxic reaction cell interactions, and proliferative responses, as affected by specific antisera to Bu-1, Th-1, Ly-4, MHC, and viral antigens.